BRIEF COMMUNICATION: The effect of growth hormone on the intracellular amino acidprofiles in the mammary gland of lactating cows

摘要

The dairy industry is a cornerstone of the New Zealand economy, and increasing milk production, especially milk protein, is essential to boost farmer profits and meet global demand for milk products. Increasing the milk protein output per unit of intake also has positive environmental effects, due to more nitrogen being partitioned towards product, rather than excreta (Pacheco & Waghorn, 2008). Amino acids (AA), particularly the nutritionally essential ones, have received attention in dairy nutritionbecause of their obvious role as substrates for protein synthesis (Lapierre et al, 2006). However, intracellular AA have also been described as important regulators of intracellular pathways controlling protein synthesis (Burgos et al. 2010). For example, the intracellular concentrations of arginine (Yao et al, 2008) and leucine (Lynch, 2001) are key regulators of the mammalian target of rapamycin (mTOR) pathway, which is involved in the control of protein synthesis and other cellular processes in multiple tissues. Our previous research indicates that mTOR signalling may regulate milk protein synthesis in the bovine mammary gland in response to growth hormone (GH) (Hayashi et al., 2009). It is not known if the GH-mediated increase in mammary protein synthesis is associated with changes in the concentration of specific intracellular AA.